1. Field of the Invention
The invention relates to inkjet printing apparatuses that print images using print heads on which pluralities of chips provided with multiple ink ejecting nozzles are aligned along the alignment direction of the nozzles, and to image processing apparatuses, etc., that process data used thereby.
2. Description of the Related Art
As for inkjet printing apparatuses, print heads are used that have ejection portions (hereafter these ejection portions will also be referred to as nozzles) that are aligned in a constant direction and that are composed of inkjet printing elements, ejection ports, and liquid paths in communication therewith. As for inkjet printing apparatuses, so-called full-line type inkjet printing apparatuses are known, which perform printing operations by way of fixing the print heads with respect to the main body of the printing apparatus and conveying the print medium in a direction that crosses the long side of the print head. Full-line type inkjet printing apparatuses are capable of forming images over the whole area of the print medium at a high speed by way of conveying the print medium in succession while printing batched 1-line image portions at the long print heads.
So-called coupled-heads are used as the print heads of such full line type inkjet printing apparatuses, which are made long by way of aligning, at a high precision, a plurality of long chips that are capable of being manufactured at a comparatively low price (refer to Japanese Patent Laid-Open No. 2006-264152). Implementing color image formation using such coupled-heads becomes possible by way of lining up a plurality of coupled-heads that correspond to inks each having different colors such as black (K), cyan (C), magenta (M), and yellow (Y), etc.
Print heads that are used in inkjet type printing apparatuses have ejection amount variations among the multiple nozzles, due to manufacturing errors, etc. When there is ejection amount variation such as this it is easy for density unevenness to occur in printed images.
Conventionally, it is known to use head shading (HS) techniques, such as that disclosed in Japanese Patent Laid-Open No. H10-13674 (1998), as processes that reduce such density unevenness. Head shading techniques correct image data according to information pertaining to the ejection amount of each nozzle. By way of this correction it is possible to increase and decrease the final number of printed ink dots, and to perform the adjustment of density in a printed image.
However, in the case where head shading techniques such as those described in Japanese Patent Laid-Open No. H10-13674 (1998) are applied to a long print head having many nozzles, because image data processing is carried out at each nozzle, a problem arises wherein a large amount of time is necessary for correction processing. There is also a problem wherein a large amount of memory capacity becomes necessary when correcting images using head shading technique, which brings about an increase in cost. Furthermore, when the resolution of the nozzles of the print head is made high, it is also required that the resolution of the detection device that detects the ejection amount of each nozzle must also be high, which also causes an increase in apparatus cost.